1. Field of the Invention
The present invention relates to a sandwich panel used as a structural member of an artificial satellite, a space antenna, or the like, and a method of manufacturing the sandwich panel.
2. Description of the Related Art
Referring to FIGS. 15 and 16, a description will be given of the structure of a conventional sandwich panel and a method of assembling the same. FIG. 15 is a diagram illustrating an example of a conventional sandwich panel fabricated by a most common manufacturing process. In addition, a sandwich panel shown in FIG. 16 is the one shown in Japanese Patent Unexamined Publication No. 275930/1992. In FIGS. 15 and 16, reference numeral 2 denotes a facing member; 3, a film-like adhesive agent; 4, a coremember; 7, an insert; 7a, an upper flange; 7b, a threaded portion; 7c, a lower flange; 8, a filler; 9, an adhesive agent; 10, a fitting hole; 11, an insert; 11a, a flange; 11b, a threaded portion; 12, a through hole; and 13, an escape. First, a description will be given of the function of the insert incorporated in the sandwich panel. In FIGS. 15 and 16, the inserts 7 and 11 have threaded holes in the threaded portions 7b and 11b. Some apparatus, though not illustrated, is generally mounted on the surface of the sandwich panel used as a structural member of a satellite. The insert serves as a threaded hole for mounting this apparatus and a grounding plate of the apparatus. Since the apparatus is generally mounted by a plurality of screws, a screw pitch must be secured with high accuracy. In addition, as can be seen from FIG. 15, the upper surface of the insert 7 is attached in such a manner as to be located at a somewhat sunken position from the facing member 2. The purpose of this is to effect the radiation of the apparatus efficiently. Namely, by causing the apparatus and the facing member 2 to be brought into close contact with each other, the heat which is generated in the apparatus is transmitted to the facing member 2, and the heat is introduced to a radiating portion by a heat pipe (not shown) incorporated in the sandwich panel. However, if the upper surface of the insert 7 projects above the facing member 2, the close contact between the apparatus and the facing 2 is prevented.
Next, a description will be given of the method of manufacturing the sandwich panel shown in FIG. 15. First, a pair of assemblies in each of which the film-like adhesive agent 3 is attached-to the facing member 2 are prepared, and the core member 4 is sandwiched by them. In this state, heat is applied from the outside while applying pressure to allow the adhesive agent 3 to cure. The fitting hole 10 is cut in the thus-prepared sandwich panel by end milling. The inside diameter of the fitting hole 10 is in a fitting relationship with the outside diameter of the upper flange 7a of the insert 7, and serves to position the insert 7.
Next, after the adhesive agent 9 is applied to the bottom of the fitting hole 10, the height of the insert 7 is made capable of being positioned at a desired position by an unillustrated jig or the like. The insert 7 is then supplied, and the adhesive agent 9 is left to cure. After the curing of the adhesive agent 9, the filler 8 is supplied through such as a hole (not shown) provided in the upper flange 7a of the insert 7. When the filler 8 cures, the insert 7 and the core member 4 are firmly secured to each other. In a case where vehement vibrations are applied such as during the launching of the satellite, the apparatus on the sandwich panel also vibrates, so that a large pulling load is applied to the insert 7. However, the reason that the sandwich panel is not broken during such a time is that the load is distributed since the pulling load acting on the insert 7 is transmitted to the core member 4 through the filler 8.
Next, referring to FIG. 16, a description will be given of a structure and a manufacturing method which are different from those of the sandwich panel shown in FIG. 15.
The insert 11 has the same function as that of the insert 7 shown in FIG. 15. The insert 11 differs greatly from the insert 7 in that the insert 11 is bonded to the reverse side of the facing member 2 and that the filler 8 is not used. Namely, the major characteristic is that the heat is distributed since the apparatus mounted on the sandwich panel can be brought into close contact with the facing member 2 at a portion other than the through hole 12 through which the fixing screw is passed and that the pulling load applied to the insert 11 is transmitted to the facing member 2 through the upper flange 11a having a large outside diameter.
Next, a description will be given of the method of manufacturing the sandwich panel shown in FIG. 16. First, the through hole 12 is cut in the facing member 2 to which the insert 11 is attached. Subsequently, the insert 11 is bonded to the facing member 2 by some method. At this time, the hole 13 is provided in advance in the core member 4 in a separate step as a space for disposing the insert 11 on the inner side of the core member 4 (this step will be referred to as that of escape machining, and the hole as the escape). In an ensuing step, the core member 4 with the escape 13 machined therein is positioned and supplied onto the facing member 2 with the insert 11 bonded thereto and the film-like adhesive agent 3, and the facing member 2 and the film-like adhesive agent 3 on the opposite side are supplied. In this state, if pressurization and heating are effected to cure the adhesive agent 3, the sandwich panel incorporating the insert 11 is formed.
With the sandwich panel of the conventional structure shown in FIG. 15 referred to above, not only is it necessary to effect assembly by using a jig or the like while exercising caution so that the upper surface of the insert does not project from the upper surface of the facing member and does not become excessively depressed, but also it is necessary to pour the filler so that voids will not be created inside. For this reason, there has been a problem in that the insert attaching operation becomes a difficult and time-consuming operation. Further, the hole for attaching the insert must be machined in the sandwich panel after the adhesive agent is cured; however, there has been a problem in that an extreme risk is entailed in the provision of mechanical processing in such a sandwich panel that a heat pipe, for instance, is embedded in its interior as with a heat pipe panel used in a structural member of a satellite. Namely, if the heat pipe becomes damaged due to poor workmanship in the hole machining, ammonia which is a deleterious substance jets out.
In addition, the insert used in the conventional structure required the lower flange portion for retaining the solidified filler to sufficiently ensure pulling strength, the upper flange for fitting to the fitting hole, and the small diameter portion which provides the space for the filler to enter and is used to reduce the weight of the insert itself. For this reason, the component shape becomes that with a large cutting allowance, so that there has been a problem in that the unit cost of the component becomes high.
Meanwhile, with the sandwich panel of the conventional structure shown in FIG. 16, not only is it necessary to effect hole cutting or escape machining before the sandwiching of both the facing member and the core member, but also it is necessary to accurately position the facing member with the insert bonded thereto and the core member provided with the escape machining. Therefore, there has been a problem in that productivity is poor. Further, since a lateral force is applied to the core in the escape machining of only the core member before sandwiching the facing member and the core member, there has been a problem in that the core is liable to become deformed, and the productivity is further aggravated.
In addition, as for the insert as well, since it is necessary to make compatible the making the weight as light as possible and the enlarging of the area of the portion coming into contact with the facing member to alleviate the shearing force, the allowance still becomes large, pushing up the unit cost.
The present invention has been devised to overcome the above-described problems, and its object is to provide a method of manufacturing a high-quality sandwich panel with high productivity by making it possible to improve the shape of the insert and its attaching method, improving the operating efficiency in the insert attaching step, and lowering the unit cost of manufacturing the insert itself.
According to a first method of the present invention, there is provided a method of manufacturing a sandwich panel in which a core member is provided between a pair of facing members, and to which an insert for mounting an apparatus thereon is attached, comprising: a first step of attaching another end portion of the insert whose one end portion is made sharp to an inner side of one of the facing members in which a hole is cut in advance; a second step of pressing the insert into the core member such that the one end portion of the insert force-cuts the core member; and a third step of attaching the other one of the facing members to a side of the core member opposing the insert-inserting side thereof.
According to a second method of the present invention, in the method of manufacturing a sandwich panel according to the first method, the one end portion of the insert is provided with a line of intersection of two planes so as to be made sharp.
According to a third method of the present invention, in the method of manufacturing a sandwich panel according to the second method, the line of intersection is provided in such a manner as to abut against the core member in parallel.
According to a fourth method of the present invention, in the method of manufacturing a sandwich panel according to the first method, the one end portion of the insert is formed in a conical shape.
According to a fifth method of the present invention, in the method of manufacturing a sandwich panel according to any one of the second to fourth methods, the line of intersection or an apex of the conical shape of the one end portion of the insert intersects with a central axis of the insert.
According to a sixth method of the present invention, in the method of manufacturing a sandwich panel according to the first method, in the first step, after the insert itself is heated, the insert is pressed against a film-like adhesive agent laid on the facing member, and a part of the film-like adhesive agent is thereby fused to bond and fix the insert to the facing member.
According to a seventh method of the present invention, in the method of manufacturing a sandwich panel according to the first method, a projecting portion is provided at the other end portion of the insert, and the projecting portion of the insert is fitted in the hole cut in the facing member in the first step so as to effect the positioning of the insert.
According to an eighth method of the present invention, in the method of manufacturing a sandwich panel according to the first method, the insert has a small-diameter portion on its side where the facing member is attached, the diameter of the small-diameter portion being smaller than that of the one end portion, an expandable adhesive agent which foams on heating is wound around the small-diameter portion before the second step, and the expandable adhesive agent is allowed to cure in the third step.
According to a ninth method of the present invention, in the method of manufacturing a sandwich panel, the insert has a flange the diameter of which is identical or substantially identical with that of one end portion of the insert on a surface attached to the facing member.
According to a tenth method of the present invention, in the method of manufacturing a sandwich panel according to the eighth method, the one end portion and the small-diameter portion of the insert are formed as separate component parts.
According to an eleventh.method of the present invention, in the method of manufacturing a sandwich panel according to the eighth method, a stepped portion or a groove portion is provided at the small-diameter portion of the insert to allow the expandable adhesive agent to flow around the stepped portion or the groove portion.
According to a twelfth method of the present invention, in the method of manufacturing a sandwich panel according to the first method, a thermosensitive material is used as the one end portion of the insert to allow the material to fill a space between the insert and the core member in the third step.
In addition, according to the present invention, there is provided a sandwich panel in which a core member is provided between a pair of facing members, and to which an insert for mounting an apparatus thereon is attached, wherein the insert is attached to an inner side of one of the facing members in which a hole is cut, an end portion of the insert on a side away from a facing-member attaching side thereof is made sharp, and the insert is attached by force-cutting the core member by the end portion.